Speed restrictions on a stretch off State Highway 1 will remain in place following an "unbelievable" offal spill stretching more than a kilometre.
The spill, about 4km north of Te Hana, completely closed SH1 on Monday evening and triggered several days work for New Zealand Transport Agency (NZTA) contractors.
The 50km/h speed restriction in the usually 100km/h zone would likely be lifted tomorrow morning.Motorists were still being advised to take care due to slippery conditions and the presence of clean-up crew.
The contractors had the delightful job of scraping the offal - 15cm deep in places - from the road with a grader. They then hosed the surface and laid a "kitty litter" grit to absorb remaining fat and improve traction, NZTA's Sarah Azam said.
"It's likely repeated treatments will be used including using an environmentally friendly wash before the road can be opened without any speed restrictions," she said.
Ms Azam said the most significant area of offal from "a mix" of animals spanned 1km, with the total area affected up to several kilometres.
The spill was in the southbound lane in the area north of Vipond Rd, between Te Hana and Kaiwaka.
Kaiwaka chief fire officer John Bowmar was among the first on the scene and described arriving to find hundreds of metres of "pure crap".
"When we first saw it we burst out laughing, it was just unbelievable. The smell was absolutely horrendous," Mr Bowmar said.
"They had said it was an offal spill but we didn't expect that. It was the across the whole lane and quite an impressive sight."
Mr Bowmar said he had returned to the scene yesterday: "It doesn't smell too bad now."
The initial spill caused significant delays for motorists, with traffic in both directions diverted through Mangawhai until Tuesday morning, at which stage the road was re-opened with a stop/go system while the cleaning continued.
Ms Azam said the road still remained "very slippery" in some sections.
"Contractors will continue to monitor the road surface and to carry out further cleaning until we are happy that it can safely be opened fully to traffic again," she said.
A police spokeswoman said the cause of the spill appeared to have been a mechanical fault with the trailer on a commercial truck.
"We are not looking at laying charges in relation to the spill, however the company involved may need to cover costs related to the clean-up," the spokeswoman said.
The NZTA had yet to calculate the cost of the clean-up but was in communication with the trucking company responsible.